Okay, so the (ahem) more credulous amongst us are all in a tizzy because Dec. 21, 2012 is the supposed date of the "Mayan Apocalypse," which is really just one drastically overhyped misinterpretation of one of several ancient Mesoamerican calendars. The odds of the Mayan Apocalypse being anything other than a New Age pseudo-science bunk are about as high as Michael Bay directing a movie with a cogent plot and no gratuitous explosions. (Read: zero.)

That said, if you're in the market for a rational cause for crippling, existential fear about the extinction of all human life, science has some wonderful new concepts with which you should become familiar. The five most terrifying are listed below.

Let's kick off our little nightmare parade with the Torino Impact Hazard Scale, a metric named for a stylish Italian burg but which actually quantifies the level of threat posed by known asteroids. A Torino 0 means the rock ain't worth a mention, because it won't ever intersect Earth. A Torino 10 means make peace with your preferred deity as it's about to rain inexorable rocky death from the skies, likely taking human civilization down in a tsunamic pyre of thunder and ash. The fact that we need a scale that goes to 10 is less than comforting. Luckily, we are aware of exactly two asteroids that rate above zero on the Torino scale — 2007 VK184 and 2011 AG5 — both of which merit a measly Torino 1. Stand down, Bruce Willis; we don't need any asteroid drillers today.

There was an exceedingly dim and disingenuous attempt recently to suggest that the Mayan Apocalypse was actually a prediction that the star Betelgeuse would go supernova in 2012, but the science of that is so bad as to be laughable. Don't get me wrong, supernovae put out a lot of energy and having one go up near the human homeworld would be bad, but it would have to be pretty near us to matter — within about 30 light-years or so, a radius that doesn't contain that many stars, let alone likely candidates to flame on supernova. (Betelgeuse is over 600 light-years distant.) And even then, what we're talking about is a stripping of the ozone layer from supernova-emitted gamma radiation output, rather than some sci-fi-esque shockwave ripping Earth apart. It wouldn't be quick or colorful, other than some nifty aurorae. You're more likely to die at the hands of Beetlejuice (or any other deranged mime and/or Tim Burton character cosplayer) than Betelgeuse or a similar supernova.

The good news is no gamma-ray burst (GRB) has ever been observed within our own galaxy. The bad news is GRBs are so powerful that they are easily observed in other galaxies, and we don't know what causes them. We think they might be products of hypernovae, the supersized cousins of supernovae, but we can't really be sure. But the fact that giant bursts of deadly radiation that dwarf supernovae can literally appear out of apparent nothingness doesn't leave us feeling all warm and cozy. If a GRB were to appear in the vicinity and direction of earth, the best case scenario is we all turn into giant green rage monsters of the Bruce Banner variety. The more likely outcome is earth is scoured clean of surface lifeforms in a blast of high-energy radiation — as we think happened 450 million years ago. Of course, since most galaxies only generate one GRB per million years, and the odds of a Milky Way GRB being aimed directly at earth are incredibly slim, there's no need for the radiation suits (or anger management classes) just yet.

The figure above is not a typo; it was the headline-grabbing 2009 statistic from Stanford professor Martin Hellman, who has spent his career modeling the likelihood of nuclear conflict. Bottom line, there are a lot of nukes lying around, and lot of countries that could build a crude nuclear weapon should they want to — some of them less than reputable. (Looking at you, North Korea and Iran.) Worst of all, once somebody sets off a nuclear weapon, the odds of a nuclear response increase dramatically, and the dominoes of mutually assured destruction start to fall — snuffing a huge swath of humanity in the process. I don't have a joke here; this one is legitimately terrifying.

Got a favorite existential threat you like to ponder on those nights when sleep comes far too easily, or just want to wrestle with the numbing dread of our own harrowing selections? Fear and loathing await in the comments section.

Editor's note: TechRepublic's Geekend blog is coming to an end this year in order for us to focus all of our resources on business technology topics. The Geekend blog has had a great run, thanks to our wonderful contributors and our loyal readers. We would love to hear which Geekend posts and/or discussions are your favorites.

About Jay Garmon

Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger — amusing and abusing IT pros. Read his full profile. You can a...

Full Bio

Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger — amusing and abusing IT pros. Read his full profile. You can also follow him on his personal blog.